Observation of the Critical State to Multiple-Type Dirac Semimetal Phases in KMgBi

TL;DR

This study demonstrates that KMgBi can transition among different Dirac semimetal phases, with experimental evidence of a flat band and tunable Dirac fermions, advancing understanding of topological phase control.

Contribution

The paper provides the first systematic experimental evidence of a critical state in KMgBi enabling transitions among multiple Dirac fermion types.

Findings

Observation of a flat band near the Fermi level.

Identification of a small bandgap (~20 meV).

Demonstration of tunable Dirac fermion phases.

Abstract

Dirac semimetals (DSMs) are classified into different phases based on the types of the Dirac fermions. Tuning the transition among different types of the Dirac fermions in one system remains challenging. Recently, KMgBi was predicted to be located at a critical state that various types of Dirac fermions can be induced owing to the existence of a flat band. Here, we carried out systematic studies on the electronic structure of KMgBi single crystal by combining angle-resolve photoemission spectroscopy (ARPES) and scanning tunneling microscopy/spectroscopy (STM/STS). The flat band was clearly observed near the Fermi level. We also revealed a small bandgap of ~ 20 meV between the flat band and the conduction band. These results demonstrate the critical state of KMgBi that transitions among various types of Dirac fermions can be tuned in one system.